Use system include <foo.h> notation for libosmocore headers

the curent local copies of libosmocore headers + source is a temporary
hack anyway. We should instead rely on a system-wide install of
libosmocore cross-compiled for arm-none-eabi.  But leave that as a
second (later) step beyond this patch.

Change-Id: Ia63fd842d45a2b404233b4326050e7eda0604cf0
diff --git a/firmware/apps/triple_play/main.c b/firmware/apps/triple_play/main.c
index 5ff3222..75fcb36 100644
--- a/firmware/apps/triple_play/main.c
+++ b/firmware/apps/triple_play/main.c
@@ -7,7 +7,7 @@
 #include "simtrace.h"
 #include "utils.h"
 #include "req_ctx.h"
-#include "osmocom/core/timer.h"
+#include <osmocom/core/timer.h>
 
 unsigned int g_unique_id[4];